The present invention concerns antibacterial and antiviral agents that are directed against tRNA targets, and methods of screening for antibacterial and antiviral agents directed against tRNA targets.
Numerous common bacteria are capable of mutating to become resistant to antibiotic agents. Viruses such as HIV are also known to mutate rapidly and thereby avoid immune defense mechanisms. Accordingly, there is a continued need for new antimicrobial agents and antiviral agents.
J. Hill et al., PCT Application WO 9705132, describe compounds that inhibit isoleucyl-tRNA synthetases. The compounds are stated to be useful against a broad spectrum of bacteria, fungi and parasites.
A first aspect of the present invention is a method of inhibiting microbe propagation. The method comprises inhibiting ribosomal binding of a specific microbial tRNA such as tRNAlysSUU, tRNAgluSUG or tRNAgluSUC (for example, at position 27-43, most preferably position 34, thereof ) in the microbe by an amount sufficient to inhibit microbe propagation. This is achieved by a drug or compound binding to positions 27-43 (one or more positions simultaneously), most preferably position 34 or 37 of the tRNA. Additionally, the compound or drug can inactive (in the microbe) one or more enzymes that are responsible for producing the modification in the specific microbial tRNA that is responsible for the specific binding properties thereof (at positions 27 to 43, preferably positions 34 or 43).
A second aspect of the present invention is a method of inhibiting retrovirus propagation in a host for that retrovirus, wherein that retrovirus primes reverse transcription by binding of a specific host tRNA to retrovirus RNA at at least a pair of separate binding sites. The method comprises inhibiting the binding of the specific host tRNA to the retrovirus RNA at one of the binding sites by an amount sufficient to inhibit propagation of the retrovirus in the host. Advantageously, mutation of the retrovirus RNA to bind an alternate host tRNA for priming of reverse transcription requires a pair of mutations at at least the pair of separate tRNA binding sites in the retrovirus RNA: a low probability event.
A third aspect of the present invention is a method of screening for compounds useful for inhibiting microbial propagation. The method comprises contacting a specific microbial tRNA (for example, tRNAlysSUU) to a ribosome that binds that tRNA in the presence of the test compound, and then determining whether the compound inhibits the binding of that tRNA (e.g., binding of tRNAlysSUU, tRNAglnSUG or tRNAgluSUC at position 27-43, most preferably position 34, thereof) to the ribosome. The inhibition of binding indicates that the test compound is useful for inhibiting microbial propagation. The test compound will generally be binding to position 27-43, individually or in combination, most preferably positions 34 and or 37 of the stated tRNAs. The screening step may be carried out in a host cell, wherein the corresponding host cell tRNA (i.e., the tRNA that binds to the same amino acid) is modified differently as compared to said microbial tRNA at position 27 through 43 thereof (i.e., has a different modification, is not modified where the microbial tRNA is modified, or has the same modification but in a structure not recognized or specifically bound by the test compound).
A fourth aspect of the invention is a method of screening for compounds useful for inhibiting retrovirus propagation in a host for the retrovirus, wherein the retrovirus primes reverse transcription in the host by binding of a specific host tRNA to retrovirus RNA at at least a pair of separate binding sites on the host tRNA. The method comprises contacting the specific host tRNA to the retrovirus RNA in the presence of the test compound, and then determining whether the compound inhibits the binding of the specific host tRNA to the retrovirus RNA in the presence of the test compound. The inhibition of binding indicates that the test compound is useful for inhibiting propagation of the virus in the host. Again, note that mutation of the retrovirus RNA to bind an alternate host tRNA for priming of reverse transcription requires at least a pair of separate mutations at different tRNA binding sites in the retrovirus RNA.